lecture 1 procon

8/3/2019 Lecture 1 Procon

1/14

Introduction toProcess Control

ChE 220


2/14

Objective

To define and determine importance ofProcess Control to Chemical Engineering

To determine the necessity of Control

To determine where Controls areneeded

Feedback and Feed forward ControlSystems


3/14

Importance of ProcessControl

Describe your method indriving a car.

Could you drive a car withoutlooking out from the windshield?

What must be provided by thecar designers?

Can a good design eliminatethe need to steer?


4/14



5/14


controlled variables - these are the variables whichquantify the performance or quality of the final

product, which are also called output variables.manipulated variables - these input variables are

adjusted dynamically to keep the controlledvariables at their set-points.

disturbance variables - these are also called "load"variables and represent input variables that cancause the controlled variables to deviate from theirrespective set points.


6/14


set-point change - implementing a change in theoperating conditions. The set-point signal is changed

and the manipulated variable is adjustedappropriately to achieve the new operatingconditions. Also called servomechanism (or "servo")control.

disturbance change - the process transient behaviorwhen a disturbance enters, also called regulatory

control or load change. A control system should beable to return each controlled variable back to itsset-point.


7/14

Feedback System


8/14

Necessity of Process Control

We want to achieve the following:

Safety

Environmental Protection

Equipment Protection

Smooth Operation

Product Quality

Profit

Monitoring and diagnosis


9/14

Where is Control Done?


10/14

Where is Control Done?


11/14

Feedback Control System

Distinguishing feature: measure the controlled variable


12/14

Feedback Control System

Advantages:

Corrective action is taken regardless of the source

of the disturbance.

Reduces sensitivity of the controlled variable todisturbances and changes in the process

(shown later).

Disadvantages:

No corrective action occurs until after thedisturbance has upset the process, that is,

until afterx differs from xsp

.

Very oscillatory responses, or even instability


13/14

Feed

Forward ControlSystem


14/14

Feed

Forward ControlSystem

Distinguishing feature: measure a disturbance

variable

Advantage:

Correct for disturbance before it upsets theprocess.

Disadvantage:

Must be able to measure the disturbance.

No corrective action for unmeasureddisturbances.

lecture 1 procon

Documents